What the Heck is an artificial neural network?

What is an artificial neural network? They supply many technologies such as Apple's A12 Bionic chip, but what are they? Forbes it breaks down.

Artificial neural networks use different layers of mathematical processing to give meaning to the information it feeds. Normally, an artificial neural network has tens of to millions of artificial neurons – called units – arranged in a series of layers. The input layer receives various forms of information from the outside world. These are the data that the network aims to process or learn.

What I find especially fascinating is how much of a black box is an ANN. This means that while it can find a mathematical function, studying the structure will not tell you what function it is trying to find out.